Opening @ Existing Concrete Column
Opening @ Existing Concrete Column
(OP)
I have a continuous reinforced concrete beam. An 8" Diameter opening was placed in the beam long after it was placed. The location of the opening is at 1/8 of the clear span of the beam. The design called for #4 @ 4" o.c. in that region. One has to assume then that the opening cut through (3) stirrups, making the spacing at that specific point equal to #4 @ 12"o.c. This obviously hurts the shear capacity of the beam, in addition to the fact that there is a probability of stress concentration and early cracking around the opening (since there is no special reinforcement to frame the opening).
A proposed solution is to fill the opening with non-shrink grout and recommend that the opening be made at the center of the beam (where stirrups are spaced at 8" o.c.). The beam will have less shear capacity still but at least it will have the concrete contribution of the shear resistance. Not sure it would solve my cracking problems around the opening though.
Any thoughts would be greatly appreciated.
A proposed solution is to fill the opening with non-shrink grout and recommend that the opening be made at the center of the beam (where stirrups are spaced at 8" o.c.). The beam will have less shear capacity still but at least it will have the concrete contribution of the shear resistance. Not sure it would solve my cracking problems around the opening though.
Any thoughts would be greatly appreciated.






RE: Opening @ Existing Concrete Column
This may not make any difference if at 2 cut (vs. 3) you still don't have the necessary shear capacity.
You could also do a re-analysis of the beam and check on the actual Vu required at the opening and compare it to the φVc with the cut stirrups.
RE: Opening @ Existing Concrete Column
Since the opening is close to the column, the shear demand is too high for #4's @ 12" o.c. to work. I have runned the calcs.
RE: Opening @ Existing Concrete Column
RE: Opening @ Existing Concrete Column
Can you add fiber, external steel, or core vertically down the center and add threaded rods with plates/nuts top and bottom?
RE: Opening @ Existing Concrete Column
RE: Opening @ Existing Concrete Column
There are different ways of upgrading an existing beam in shear..
As suggested above, FRP wrap is one of them. You could use steel plates / channels on each side of the beam and above / below the opening as required.
You could reduce the span of the beam by adding a diagonal brace or by steel beam bolted to the column and the beam on the other side. Of course, the capacity of the column also would have to be cheched.